Refrigeration



Jan. 30, 1945. P. EDBERG 2,368,455

REFRIGERATION Filed Sept. 25, 1941 2 Sheets-Sheet 1 BY fiILNVZENTORZWMZZW M ATTORNEY Jan. 30, 1945. P. EDBERG 2,368,455

REFRIGERATION Filed Sept. 25, 1941 2 Sheets-Sheet 2 INVENTOR BY (a lfimM ATTORNEY Patented Jan. 30, 1945 nnrmeeaarron Per Edberg, Evansville,Incl, asalgnor to Servel,

Inc., New York, N. Y., a corporation of Delaware Application September25,1941, Serial No. 412,228

9 Claims. (Cl. 52-119) My invention relates to refrigeration, and moreparticularly to splitting or dividing of liquid in refrigeration systemsinto a plurality of paths of flow.

It is often desirable in refrigeration systems to divide a stream ofliquid into a plurality of paths of flow. This is especially true inabsorption refrigeration systems of large size, because in suchinstances the manner in which liquid flow is effected determines to agreat.

extent the efllciency and capacity of a system, the arrangement ofcomponent parts of a system, and the amount of space a system of a givencapacity will occupy.

In accordance with the invention liquid flowing in a refrigeratingsystem operating at exextremely' low pressures is divided into aplurality of paths of flow through several tubes in each of which theliquid flows upwardly. While the tubes employed to provide the severalpaths of flow offer substantially no resistance to flow of liquid, thefact that the several streams of liquid flow to a region at which thevapor pressure is less than the vapor pressure of the liquid in theseveral streams causes some of the upwardly flowing liquid to vaporize,whereby the liquid entering the region is partially cooled down toward atemperatur corresponding to the vapor pressure existing at the region.The vapor formed in the tubes builds up resistance to flow of liquidwhich is advantageously utilized to bring about proper division ofliquid into the several paths of flow, that is, vapor may form at thesame time or alternately in the different tubes so that over a period oftime the desired quantity of liquid flows through each of the severalpaths of flow.

Dividing liquid in the manner just described lends itself to anarrangement whereby a flash chamber can be provided at the region towhich the several streams of liquid are introduced, so that furthervaporization of liquid can take place in such chamber without affectingthe subdivision of liquid into the several paths of flow. With suchvaporization of liquid in the flash chamber additional cooling of liquidis effected to bring the liquid down to a temperature corresponding tothe vapor pressure existing at the region.

It is, therefore, an object of the invention to provide in an absorptionrefrigeration system an improved liquid divider of the character lustdescribed.

The novel features which I- believe to be characteristic of my inventionare set forth with particularity in the claims. The invention, both asto organization and method, together with the above and other objectsand advantages thereof, will be better understood as I next describe myimproved liquid divider embodied in an absorption refrigeration systemlike that described in application Serial No. 239,762 of A. R. Thomasand P. P. Anderson, Jr., filed November 10, 1938, now Patent No.2,282,503 granted May 12, 1942.

In the accompanying drawings forming a part of this specification, I

Fig. 1 more or less diagrammatically illustrates an absorptionrefrigeration system in which is embodied a liquid divider embodying myinvention;

Fig. 2 is an enlarged fragmentary view taken at line 2-2 of Fig. 3,partly in section, to illustrate the manner in which several streams ofliquid.- are introduced into the upper part of the evaporator shown inFig. 1;.

Fig. 3 is a vertical view of an end of the evaporator shown in Fig. 1,partly broken away and in section, to illustrate more clearly the mannerin which flow of liquid is effected in the evaporator;

Fig. 4 is a vertical view, partly in section, taken at line 4-4 ofFig.3;

Fig. 5 is a horizontal sectional view,.taken at line 5-5 of Fig. 6, toillustrate the flash chamber associated with the evaporator shown inFig. 1 and into which several streams of liquid flow;

and

Fig. 6 is a vertical sectional view, taken at line 6-6 of Fig. 5, toillustrate the flash chamber more clearly.

Referring to Fig. 1, the .invention is embodied in a two-pressureabsorption refrigeration system like that described in the Thomas andAnderson application referred to above. A system of this typeoperates atlow pressures and includes a generator or vapor expeller III, acondenser ll, an evaporator l2, and an absorber ll which areinterconnected in such a manner that the pressure differential in thesystem is maintained by liquid columns.

The disclosure in the aforementioned Thomas and Anderson application maybe considered as being incorporated in this application, and, ifdesired, reference may be made thereto for a detailed description of therefrigeration system. In Fig. 1 the generator ll inclues. an outer shell15 within which are disposed a plurality of veriical riser tubes l6having the lower ends thereof communicating with a. space I! and theupper ends thereof extending into and above the bottom of a vessel [8.The space H! surround- 1111; the tubes IS in shell 15 forms a chamber 19to which steam is supplied through a conduit 20. The chamber is providesfor full length heating of the tubes 3 with the toppart of the chamherbeing vented at 2| to atmosphere. A conduit 22 is connected to thebottom part of shell 15 for draining condensate from chamber [9.

The system operates at a partial vacuum and may contain a water solutionof refrigerant in absorption liquid, such as, for example, a watersolution of lithium chloride or lithium bromide or a suitable mixture ofsuch salts. With steam being supplied to chamber I! through conduit 20at atmospheric pressure, heat is applied to tubes l whereby water vaporis expelled from solution, such expelled vapor being efl'ective to raiseliquid absorbent by gas or vapor-lift action with the expelled watervapor forming a central core within an upwardly rising annulus of theliquid. The expelled vapor passes from the upper ends of the tubes l6into the vessel l8, and thence flows through a conduit 23 into condenserII in which the expelled vapor is liquefied. The condensate formed incondenser II flows through a conduit 24, vessel 25, riser imbes 26v and21, flash chamber 28 and conduits 29 and 30 to the top part ofevaporator l2, as will be described presently.

The refrigerant evaporates in evaporator l2 to produce a refrigeratingor cooling eifect with consequent absorption of heat from thesurroundings, as from a stream of air flowing over the exterior surfacesof the evaporator. The refrigerant vapor formed in evaporator l2 flowstherefrom to the absorber l4 into which absorption liquid is introducedat the top part through a conduit 3|. The entering absorption liquidflows into a vessel 32 in which liquid is distributed laterally orcrosswise of a plurality of vertically disposed pipe banks 33 which arearranged alongside each other. The liquid flows from the center part ofvessel 33 into laterally disposed end chambers 34 and thence throughconduits 35 into a plurality of liquid holders and distributors 35 whichextend lengthwise of and above the uppermost horizontal tubes of pipebanks 33. Absorption liquid is siphoned over the walls of the liquidholders 36 to efiect complete wetting of the uppermost horizontal tubes.Liquid drips from each horizontal tube onto the next lower tube wherebyall of the tubes are wetted with a film of liquid.

The refrigerant vapor formed in evaporator l2 passes through end headers31 into the absorber l4 in which the vapor is absorbed into theabsorption liquid. The absorption liquid is conducted from absorber I4through a conduit 38, a first passage in liquid heat exchanger 39,conduit 40, vessel 4|, and conduit 40, vessel 4|. and conduit 42 intospace ll of generator l0.

'Reirigerant vapor is expelled out of solution ascaess absorber M. Thiscirculation of absorption liquid results from the raising of liquid inriser tubes l5 whereby the liquid can flow to absorber l4 and returnfrom the latter to generator in by force of gravity. The upper part ofvessel 3! and vessel I8 are connected by a conduit 44, so that thepressure in vessel 8! is equalized with the pressure in the top part ofgenerator I 0 and condenser I.

The absorber I4 and condenser H constitute heat rejecting parts of therefrigeration system and are cooled by a suitable cooling fluid, such aswater, for example, which enters the bottom parts of the pipe banks 33through a conduit 45 and manifold 46 and leaves the top parts of thepipe banks through a manifold 41 and conduit 48. The conduit 48 isconnected to condenser ll whereby the same cooling fluid can be utilizedto cool the absorber I4 and condenser H, the cooling fluid then leavingthe condenser through a conduit 43.

The system operates at low pressures with the generator Ill andcondenser ll operating at one pressure and the evaporator 12 andabsorber l4 operating at a lower pressure, the pressure differentialtherebetween being maintained by liquid columns. Thus, the liquid in theU-trap formed by conduit 24, vessel 25 and riser tubes 26 and 21maintains the pressure differential between condenser H and evaporatorl2, the liquid column in conduit 33 maintains the pressure differentialbetween the outlet of absorber l4 and generator Ill, and the liquidcolumn formed in conduit 3| maintains the pressure difie'rential betweenthe inlet of absorber l4 and the upper part of generator HI. Duringoperation of the system, the liquid columns may form in conduits 38, 43and 24 to the levels 2:, y and z, for example.

The evaporator l2 includes a plurality of horizontal tubes 50 to whichare secured a plurality of heat transfer flns 5|. The ends of tubes 50pass through and are secured in openings formed in headers 31 at eachend of the evaporator. The liquid flowing to evaporator l2 throughconduits 29 and 30 is conducted to liquid holders 52 and 53 located inthe top part of one of the headers 31. The liquid holders 52 and 53 areconnected to and supported by two of the uppermost horizontal tubes 50.

The tubes 50 are connected at their ends to provide two separate pathsof flow for the liquid introduced into the holders 52 and 53. Referringmore particularly to Fig. 3, the two right-hand banks of tubes 50 form afirst path of flow for liquid and the three left-hand banks of tubesform a second path of flow for liquid. In the path of flow formed by thetwo right-hand banks of tubes. liquid flows through successively lowertubes in the two banks through suitable end connections. This isaccomplished by providing at the ends of end tubes 50 open top buckets54 each formed with an opening in a bottom part thereof to receive anend of a tube 50 in one of the banks of tubes. The buckets 54 are alsonotched to receive an end of the next higher tube 50 in the other bankof tubes forming a part of the path of flow being described.

In the path of flow formed by the three lefthand banks of tubes 50, opentop buckets 55 and 56 are provided in the headers 31'. These buckets aregenerally similar to the buckets 55 with openings or notches formed inboth ends to receive the ends of tubes 50 in difl'erent banks of tubes.

The buckets l8 and 88 serve as connections through which liquid isdirected and qaused'to flow through successively lower tube?" in the;

three left-hand banks of tubes.

The two paths of flow for liquid formed by the tubes 68 are indicated asA and B in Fig. 2

. to which liquid is supplied from the liquid holders and 68. Nobarriers or dams of any kind are provided in tubes 50 to cause shallowpools of liquid to be formed therein. The tubes 68 are as level aspossible and the liquid ,merely trickles along the bottom parts thereof.The tubes are preferably grooved to provide small capillary passages atright angles to the lengths of the tubes, so that complete wetting ofthe inside walls of the tubes is effected in the manner de-- scribed inO'Brien application Serial No. 411,459, filed September 19, 1941.vaporization of refrigerant takes place in tubes 56 with consequentabsorption of heat from the surroundings, as explained above.Refrigerant vapor flows out of II is condensed in condenser H and flowsthrough conduit 28 into vessel 26, and thence divides intotwo paths offlow in riser tubes 28 and 21. The vessel 26 serves to reduce thevelocity pressure of the liquid before division of liquid is eifectedinto the riser tubes 26 and 21. The liquid from riser tube 21 enters oneof the spaces 62 in flash chamber 28 from which it flows through conduit26 to the liquid holder 62. Likewise, the liquid from riser tube 26enters the other space 62 in flash chamber 28 from which it flowsthrough conduit 30 to'the other liquid holder 58.

, rator 12 are so located and positioned that, when tubes 60 and fromthe open top buckets 64, 66,

and 56 into the headers 31 from which the vapor passes into absorber Mfor absorption by the absorption solution. Liquid refrigerant passesfrom each tube 50 to the next lower tube in its path of flow, and anyrefrigerant discharged from the lowermost tubes 50 in the two paths offlow A and B passes directly into absorber ll.

Referring to Fig. 2, the arrows indicate the direction in which a streamof air is caused to flow over the surfaces of tubes 50 and heat transfer flns 5| of evaporator l2. The stream of air first ilows past the twobanks of tubes forming the path of flow A and then past the three banksof tubes forming the path of flow B. The air is warmest when it comes inthermal 0on tact with the tubes forming the path of flow A and, aftercoolingof air is effected by the first two banks of tubes, air at alower temperature comes in thermal contact with the remaining threebanks of tubes forming the path of flow B.

In order to deliver liquid from condenser l I to both liquid holders 52and 53 in evaporator l2, the liquid flowing from the condenser H issplit or divided into a plurality of paths of flow by connecting conduit24 t the bottom partof a vessel 25 and connecting two upwardly extendingriser tubes 26 and 21 to the upper part of this vessel.

The upper ends of riser tubes 26 and 21 are connected to the bottom partof another vessel 28 which serves as a flash chamber and within which isprovided a dividing wall or partition 60.

To the top edge of partition 60 is fixed a baille plate 6| havingoppositely inclined sides which the columns of liquid built up in theup-legs or riser tubes 26 and 21 of the U -trap formed by the partsconnecting the condenser II and evaporator I2, liquid will alwaysoverflow into the liquid holders 52 and 53 from the liquid columns atthe upper ends of riser tubes 26 and 21 for any pressure differentialbetween evaporator l2 and condenser ll ranging from zero to maximum.Stated another way, when operation of the system is first started andthe pressure differential between condenser H and evaporator 12 is zero,the column of, liquid formed in conduit 24 will be sufllciently high tocause condensate to overflow by gravity from the upper ends of risertubes 26 and 21 into the upper part of evaporator l2. After the pressurediiferential builds up in the system so that the pressures in condenserll andevaporator l2 are in the neighborhood of mm. and 9 mm. mencury,for example, and the liquid level in conduit 28 is at some point, suchas 2, liquid will still flow by gravity from the condenser to theevaporator by overflowing into the latter from the upper ends of risertubes -26 and 21.

Since the condensate flowing from condenser II to evaporator 12 ispassing from the high to extend downwardly into each of the spaces 62 atopposite sides of the partition. Below each side of baille plate 6| asecond baffle plate 63 is disposed in each of the spaces 62, as shownmost clearly in Fig. 6. A pipe 64 is connected at its upper end to theflash chamber 28 and at its lower end to one of the headers 31of-evaporator l2. 6

Referring more particularly to Figs. 5 and 6, it will be seen that theupper endsof riser tubes 26 and 21 and also conduits 29 and areconnected to spaces 62 at opposite sides of the partition 60. The lowerends of conduit 29 and 20 are connected to the liquid holders 52 and 63,as explained above.

During operation of the refrigerationsystem, assuming that the system ischarged with a water solution of a lithium salt, for example, watervapor expelled from solution in generator the low pressure side of thesystem, and the system is operating at extremely low pressures and at apartial vacuum, there is a tendency for liquid to vaporize in risertubes 26 and 21 due to decrease in pressure on the rising liquidtherein. With vaporization of liquid occurring in the riser tubes 26 and21 some cooling of liquid is effected on its way to evaporator 12.However, when the liquid enters flash chamber 28 associated withevaporator l2, the liquid usually has not cooled down to a temperaturecorresponding to the vapor pressure in the evaporator. The flash chamber28 is provided .so that vaporization of liquid can take place thereinwithout disturbing the flow of liquid in the evaporator. This willreadily be appreciated when consideration is given to the fact that in asystem like that described, with the evaporator at a temperature ofabout 50 F. and at a pressure of approximately 9 mm. mercury, the ratioof vapor volume to liquid volume is on the order of 100,000 to 1', sothat a small amount of liquid evaporating forms a lot of vapor. Underthese conditions the refrigerant supplied to the evaporator changes fromliquid to gas phase by vaporization which is in the nature of boiling ascontrasted with the manner in which evaporation of liquid takes placesolely by surface phenomenon.

The flash chamber 28 serves as a precooler for liquid flowing toevaporator 12, the heat of cooling of the liquid. The bames GI and iiare provided to separate any liquid spray from vapor that passes throughpipe 64,. because entrainment of liquid with vapor flowing through thispipe constitutes a loss of such liquid.

By introducing liquid into the evaporator in several paths of flow, thatis, at opposite sides of partition 60 in flash chamber 28, no upset ofliquid division can take place due to formation of vapor in the flashchamber. The liquid remains divided in the spaces 82 and flows fromthese separate spaces through conduits 29 and 30 into the liquid holders52 and 53. It has been found that with this arrangement the liquid iscooled sufficiently in the flash chamber so that when it enters theliquid holders 52 and 53, the liquid is at a temperature correspondingto the vapor pressure in the evaporator.

When a single stream is split and divided into a plurality of streams inwhich equal division of liquid flow is desired, it is usually extremelyimportant that the split streams ofler identically the same resistanceto flow of liquid. If there is any unbalance or difference in theresistance offered to liquid how in the several streams, then a greateramount of liquid will tend to flow through the stream offering thelesser resistance to liquid flow.

In the liquid divider provided the riser tubes 26 and 21 are of suchsize that there is substantially no resistance to flow of liquid.However, the vapor formin in the tubes 26 and 21 does build upresistance to flow of liquid which is appreciably greater and clearlydominates the negligible resistance to liquid flow produced by the tubesthemselves. Vapor may form at the same time or alternately in the tubes26 and al to build up resistance to liquid flow, with the result thatover a period of time substantially equal division of liquid flow in thetubes is efiected. Hence, in the event there is a tendency for a greateramount of liquid to flow through one riser tube than the other, evenwith the tubes being approximately the same: size, the resistance toliquid flow resulting from formation of vapor in the tubes counteractsany tendency for unequal division of liquid to occur, whereby the vaporis efiectively utilized to cause and bring about proper division ofliquid.

In view of the foregoing, it will be understood that steady and constantflow of liquid does not occur in riser tubes 26 and 21. The action thattakes place may be likened to that of several geysers in which violentboiling of relatively small amounts of liquid occurs to producerelatively large volumes of vapor. This is due to the fact that theliquid risingin tubes 26 and 27 tends to remain as liquid above itsboiling temperature, and when vaporization does occur it isinstantaneous and sudden. With the occurrence of each geyser effect somewater is pushed from the upper ends of riser tubes 28 and 27 so that thepressure at any region in the liquid columns becomes reduced to bringabout a condition in which more boiling and vaporization of liquid isefiected. As pointed out above. it is the forming of vapor in the mannerjust described that builds up momentary resistance to liquid flow whichis intermittent in character and suflicient to insure that substantiallyequal division of liquid flow is effected through the tubes 26 and 2?.

With approximately half of the liquid being supplied to each of theliquid holders 52 and 53, it will now be understood that the path of howA uses up such a quantity of the liquid that it adequately takes care ofthe two banks of tubes forming this path of flow. While the path of flowB is supplied with the remaining half of the liquid, this amount ofliquid adequately takes care of three banks of tubes because the air isat a lower temperature when it comes in contact with the banks of tubesforming the path of flow B.

In view of the foregoing, it will now be understood that partialvaporization of liquid in the upper parts of riser tubes 26 and 21 isthe main factor eilecting regulation of liquid flow in these risertubes. With liquid being supplied from the same source to riser tubes 26and 21, the quantity of vapor formed in each riser tube will be the sameas in the other because the initial temperature of the liquid enteringthe tubes is the same and the reduction in pressure is the same throughthe parallel paths of flow.

By employing tubes of diiIerent size so that unequal resistance to flowof liquid is built up by the vapor formed in the riser tubes, apredetermined unequal division of liquid can be effected. When equaldivision of liquid is desired, riser tubes of substantially the samesize are employed with the tubes in effect constituting long orifices.The formation of vapor increases the resistance to liquid flow to suchan extent that the small difierence between individual tube resistancesdoes not appreciably affect the division of liquid.

While a single embodiment of the invention has been shown and described,it will be ap parent that modifications and changes may be made withoutdeparting from the spirit and scope of the invention, as pointed out inthe following claims.

What is claimed is:

1. A multi-pressure absorption refrigeration system having a generatorand a condenser adapted to operate at one pressure and an evaporator andan absorber adapted to operate at a lower pressure, and connections forthe aforementioned parts to provide circuits for circulation ofrefrigerant and absorption liquid, the connection through which liquidis conducted from the condenser to the evaporator including a U-traphaving a down-leg and an up-leg comprising a plurality of parallelbranches for supplying liquid to difl'erent parts of the evaporator,said parts and connections being so constructed and arranged that theliquid flowing into said branches has a vapor pressure greater than thevapor pressure in the evaporator whereby vaporization of liquid takesplace in said branches to produce vapor blocking therein to promotedivision of liquid into the branches.

2. A multi-pressure absorption refrigeration system having a generatorand a condenser adapted to operate at one pressure and an evaporator andan absorber adapted to operate at a lower pressure, and connections forthe aforementioned parts to provide circuits for circulatlon ofrefrigerant and absorption liquid including conduit means to form liquidcolumns to maintain the pressure difierential, the part of said conduitmeans through which liquid is conducted from the condenser to theevaporator including a U-trap having a down-leg and an upleg comprisinga plurality of branches into which upwardly rising liquid is dividedinto a plurality of paths of flow for supplying liquid to differentparts of the evaporator, the system being so constructed and arrangedthat for the pressure existing in the evaporator vaporization of liquidtherein is in the nature of boiling as contrasted with the phenomenon ofsurface evaporization, whereby liquid rising in said branches andflowing thereto from the condenser vaporizes to produce vapor blockingto promote and bring about dividing of liquid into said branches.

3. An absorption refrigeration system having a condenser adapted tooperate at one pressure and an evaporator adapted to operate at a lowerpressure, a U-trap connecting said condenser and said evaporator throughwhich liquid flows from the former to the latter, said U-trap havingsubstantially no resistance to liquid flow and serving to form a liquidcolumn to maintain the pressure diiferential between the evaporator andcondenser, the system with which the condenser and evaporator areassociated being such that vaporization of liquid in the evaporator isin the nature of boiling as contrasted with the phenomenon of surfaceevaporation, and said U-trap including a plurality of parallel branchesin the up-leg thereof whereby liquid is divided into a plurality ofpaths of flow in each of which liquid flows upwardly, and said U-trapbeing so constructed and arranged that vapor forms in said branches toproduce vapor blocking to promote distribution of liquid into theseveral paths of flow.

4,. A multi-pressure absorption refrigeration system having acondenseradapted to operate at one pressure and an evaporator adapted to operateat a lower pressure such that vaporization of liquid therein is in thenature of boiling as contrasted with the phenomenon of surfaceevaporation, -a U-trap and a flash chamber associated with theevaporator and through which liquid is conducted from the condenser tothe evaporator, said flash chamber having a plurality of spaces in vaporcommunication with the evaporator and from which liquid flows by gravityto different parts of the evaporator, and structure for subdividingliquid flowing from the condenser including a plurality of riser tubesconnected in parallel in the up-leg of said U-trap with the upper endsof said tubes being in communication with the spaces in said flashchamber, said structure being so constructed and arranged that theliquid flowing upwardly in said riser tubes has a vapor pressure greaterthan the vapor pressure in the evaporator whereby vaporization of liquidis effected to produce vapor blocking in said riser tubes to promotedividing of liquid into the latter, and said flash chamber beingprovided to serve as a region in which vapor flashing may occur to coolthe liquid to a temperature corresponding to the vapor pressure in theevaporator without disturbing the dividing of liquid efiected by saidriser tubes. 1

5. An absorption refrigeration system in which flow of refrigerant iseffected and including an evaporator adapted to operate at such apressure that vaporization of refrigerant therein is in the nature ofboiling as contrasted with the -phe nomenon of surface evaporation, aflash chamber in vapor communication with said evaporator, structureincluding said flash chamber for subdividing refrigerant flowing in thesystem into several paths of flow to supply refrigerant to a pluralityof parts of the evaporator, said structure being so constructed andarranged that vapor blocking is utilized in said several paths of flowto promote division of liquid therebetween, and said flash chamber beingassociated with said evaporator and arranged in said refrigerantdividing structure in such a manner that vapor 6. In a refrigerationsystem in which circ'ula- 2 tion of liquid is effected, such systemincluding a first part and a plurality of places which receive liquidfrom said first part, the pressure existing in said flrst part beinghigher than the pressures existing in said places during operation ofthe system; structure including a plurality of riser tubes connectingsaid part and said places for dividing and conducting liquid from saidpart in a plurality of paths of flow to said places, said structureforming a downleg and an up-leg through which the liquid flows to formliquid columns to maintain the pressure differential between said partand said places, said riser tubes having vapor formed therein by heatderived from the liquid as the liquid passesv through progressivelylower regions of pressure in said paths of flow, and said structurebeing so constructed and arranged that said vapor is utilized to retardthe rate at which liquid flows into said riser tubes to promote dividingof the liquid between said paths of flow.

7. In an absorption refrigeration system in which circulation of liquidis effected, such system including a condenser and evaporator structure;means including a, plurality ofsriser tubes connecting said condenserand said evaporator structure for dividing and conducting liquid fromsaid condenser in a plurality of paths of flow to different places insaid evaporator structure, the pressure existing in said condenser beinghigher than the pressure existing in said evaporator structure duringoperation of the system, said connecting means including said risertubes forming a down-leg and a plurality of up-legs throughwhich theliquid flows to form liquid columns to maintain the pressuredifferential between said'condenser and said evaporator structure, saidriser tubes having vapor formed therein intermittently by suddenvaporization of small amounts of liquid due to the liquid tending toremain in a liquid phase above the boiling temperature while passingupwardly through progressively lower regions of pressure in said risertubes, and said means being so constructed and arranged that said vaporis utilized to retard the rate at which liquid flows into said risertubes to promote dividing of the liquid between said paths of flow.

8. A two-pressure absorption refrigeration system of the type whichoperates in a partial vacuum and having a generator and condenseradapted to operate'at one pressure and an evaporator and an absorberadapted to operate at a lower pressure, and connections fo'rtheaforementioned parts to provide circuits for circulation of refrigerantand absorption liquid, the connection through which liquid is conductedfrom the condenser to the evaporator including a plurality of parallelbranches for supplying liquid to different parts of the evaporator andproviding liquid columns to maintain the pressure difierential, saidparts and connection being so constructed and arranged that the liquidflowing into said branches has a vapor pressure greater. than the vaporpressure in the evaporator whereby vaporization of liquid takes place insaid branches to produce vapor blocking therein to promote division ofliquid into the branches. 1

erant and a saline solution as an absorbent, a

generator and condenser adapted to operate at 6 ascents one pressure andan evaporator and absorber adapted to operate at a lower pressure, andconnections for the aforementioned parts to provide circuits forcirculation of refrigerant; and ab sorption liquid, the connectionthrough which 5 liquidds conducted from the condenser to the evaporatorincluding a plurality of parallel branches for supplying liquid todifferent parts of the evaporator and providing liquid columns tomaintain the pressure difierential, said parts

